You've probably seen that infamous photo of Madison Square Garden from 1939, where over 20,000 American Nazis held a "patriotic" rally in New York. But a new 7-minute documentary gives us an even more detailed (and terrifying) peek at just what happened that night on February 20, 1939.

The documentary, produced by Field of Vision and directed by two-time Oscar nominee Marshall Curry, collects for the first time all the known footage of the event. And it's really quite fascinating to watch Nazis pledge their undying allegiance to the American flag one minute, and give a Nazi salute the next.

"When I found out that it had been filmed, I asked an archival researcher, Rich Remsberg, to see what he could find," Curry says in a new Q&amp;A about the film.

"It turned out that short clips had been used in history documentaries before, but no one seemed to have collected together all of the scraps of footage — there was some at the National Archives, some at UCLA's archive, some at other places," Curry continued.

The entire 7-minute film is available for free on Vimeo. And it's really quite a disturbing artifact from an era when far too many Americans were cosy with the Nazi regime.

The documentary is simple, but there's also a good deal of artistry in not only the music, but the ways in which the shots are presented.

When a protester storms the stage the first thing you notice is the obvious savagery of the Nazis beating up the man. But the director zooms in on things to help focus your eye, and the less obvious becomes even more grotesque. Case in point, we see a young Nazi child mock the way that the man ran, clearly delighted that there was violence happening just a few feet away.

And the slow motion take of the protester being both beat up and carted away is devastating for those of us in 2017 who know that the brutal torture and murder of the Nazi concentration camps are well underway across the Atlantic.

"We'd like to think that when Nazism rose up, all Americans were instantly appalled," Curry says about the era. "But while the vast majority of Americans were appalled by the Nazis, there was also a significant group of Americans who were sympathetic to their white supremacist, anti-Semitic message."

If you're interested in learning more about the video you can read an interview with director Marshall Curry here.

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